1. Field of the Invention
The present invention relates to a plasma display panel. More particularly, the present invention relates to a plasma display panel with an improved structure that can enhance brightness, and can enhance contrast, for example, when a plasma display panel is operated in a brightly lit room.
2. Description of the Related Art
A plasma display panel (PDP) is an apparatus to form an image using an electrical discharge. Its superior performance in terms of brightness and viewing angle has ensured its popularity. In such a PDP, a DC or AC voltage applied to electrodes causes a gas discharge between the electrodes, and ultraviolet rays generated by the discharge excite a fluorescent material, which emits a visible light.
PDPs are classified as either a DC type or an AC type, according to the type of discharge. The DC type PDP has a structure in which all electrodes are exposed to a discharge space, and charges move directly between the electrodes. The AC type PDP has a structure in which at least one electrode is covered with a dielectric layer, and charges do not move directly between the corresponding electrodes but discharge is performed by wall charges.
Also, PDPs may be classified as a facing discharge type or a surface discharge type, according to the arrangement of the electrodes. The facing discharge type PDP has a structure in which a pair of sustain electrodes are formed respectively on an upper substrate and a lower substrate, and discharge occurs perpendicular to the substrate. The surface discharge type PDP has a structure in which a pair of sustain electrodes are formed on the same substrate, and discharge occurs parallel to the substrate.
The facing discharge type PDP has a high luminous efficiency, but a disadvantage being that the fluorescent layer is easily deteriorated. For this reason, the surface discharge type PDP is presently more common.
FIGS. 1 and 2 show the construction of a conventional surface discharge type PDP. In FIG. 2, the upper substrate 20 is shown rotated by 90 degrees for easier understanding of the inner structure of the PDP.
Referring to FIGS. 1 and 2, the conventional PDP includes a lower substrate 10 and an upper substrate 20 facing each other.
On the upper surface of the lower substrate 10, a plurality of address electrodes 11 are arranged in a stripe configuration. The address electrodes 11 are covered by a first dielectric layer 12 (preferably white). On the first dielectric layer 12, a plurality of barrier ribs 13 are formed at a predetermined spacing to prevent electrical and optical cross-talk between discharge cells 14. On the inner surfaces of the discharge cells 14, which are partitioned by the barrier ribs 13, a red (R), green (G) and blue (B) fluorescent layer 15 is coated to a predetermined thickness. The discharge cells 14 are filled with a discharge gas, which is typically a mixture of neon (Ne) and a small amount of xenon (Xe), as is generally used for plasma discharge.
The upper substrate 20 is a transparent substrate, which transmits visible light, and is preferably made of glass. The upper substrate 20 is coupled to the lower substrate 10 having the barrier ribs 13. On the lower surface of the upper substrate 20, sustaining electrodes 21a and 21b are formed in pairs and are perpendicular to the address electrodes 11 and are arranged in a stripe configuration. The sustaining electrodes 21a and 21b are formed of a transparent conductive material, such as indium tin oxide (ITO), to transmit visible light. In order to reduce the line resistance of the sustaining electrodes 21a and 21b, bus electrodes 22a and 22b are formed of a metal, on the lower surface of the respective sustaining electrodes 21a and 21b, to a width less than that of the sustaining electrodes 21a and 21b. These sustaining electrodes 21a and 21b and the bus electrodes 22a and 22b are covered with a transparent second dielectric layer 23. On the lower surface of the second dielectric layer 23, a protective layer 24 is formed. The protective layer 24 prevents the second dielectric layer 23 from damage by plasma sputtering, and emits secondary electrons, thereby lowering discharge voltages. The protective layer 24 is generally formed of magnesium oxide (MgO). A plurality of black stripes 30 are formed at a predetermined spacing, parallel to the sustaining electrodes 21a and 21b, on the upper surface of the upper substrate 20, to prevent external light from entering the panel.
The conventional PDP constructed as above generally uses a cycle of two operations: address discharge and sustaining discharge. The address discharge occurs between the address electrode 11 and any one of the sustaining electrodes 21a and 21b, and during the address discharge, wall charges are formed. The sustaining discharge is caused by a potential difference between the sustaining electrodes 21a and 21b positioned at the discharge cells 14 in which the wall charges are formed. During the sustaining discharge, the florescent layer 15 of the corresponding discharge cell is excited by ultraviolet rays generated from the discharge gas, emitting visible lights. The visible light emitted through the upper substrate 20 form the image.
However, when the conventional PDP constructed as above is used in brightly lit room conditions, external light enters the discharge cells 14, mixing with the light generated by the discharge cells 14. This lowers the contrast and reduces the image display performance of the PDP when used in a brightly lit room.